mediatek: UniFi 6 LR: disable RTC

There is not RTC battery connected to the SoC of the UniFi 6 LR board.
Disable the RTC to prevent the system coming up with time set to
2000-01-01 00:00:00 after each reboot.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/dts/mt7622-ubnt-unifi-6-lr.dtsi

@@ -203,6 +203,12 @@
 	};
 };
 
+&rtc {
+	status = "disabled";
+
+	/* No RTC battery */
+};
+
 &uart0 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&uart0_pins>;